Work will continue on the mode of action of peptide Al of cholera toxin. In the presence of GTP and a soluble protein, it catalyses the transfer of ADP-ribose from NAD to a number of membrane-bound and soluble erythrocyte proteins. The principal target is the GTP-binding component of adenylate cyclase. We intend to quantitate this protein and to begin to purify it. We also intend to investigate the nature of the other target proteins & the possible physiological changes of their ADP-ribosylation. We shall extend our observations to other cell types.